title: Enantioselective synthesis of alkyne-substituted quaternary carbon stereogenic centers through NHC-Cu-catalyzed allylic substitution reactions with (i-Bu)2(alkynyl)aluminum reagents.
abstract: A catalytic enantioselective method for the formation of alkyne-substituted all-carbon quaternary stereogenic centers is reported. Additions of alkynylaluminums to alkyl-, aryl-, carboxylic ester-, or silyl-substituted allylic phosphates are promoted by 1.0-5.0 mol % loadings of NHC-Cu complexes derived from air-stable and commercially available CuCl(2)·2H(2)O. The requisite Al-based reagents are prepared through treatment of the corresponding aryl-, heteroaryl-, alkyl-, or alkenyl-substituted terminal alkynes with diisobutylaluminum hydride in the presence of 5.0 mol % Et(3)N at ambient temperature. The desired 1,4-enynes are obtained in up to 98% yield and >99:1 enantiomeric ratio. Selected Au-catalyzed cyclizations involving the alkyne unit of the enantiomerically enriched products are presented as a demonstration of the method's utility in chemical synthesis.
authors.affiliation: Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Dabrowski
authors.forename: Fang
authors.initials: F
authors.lastname: Gao
authors.forename: Amir H
authors.initials: AH
authors.lastname: Hoveyda
mesh_terms: D000480:Alkynes / Q000138:chemical synthesis* / Q000737:chemistry; D000535:Aluminum / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000480:Alkynes; D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; C030011:carbene; D003300:Copper; D000535:Aluminum; D008697:Methane